It is better and much easier on the server if you leave the dowel *taller* than the total height of the cake - at least 1" so once you are at the venue it can be removed. The *only* purpose of that center dowel is to help hold the tiers from sliding apart during transportation. Leaving it in makes it hard for the server to take the tiers apart Hide the hole w/icing OR a flower or leaf or fill in w/icing.
It is soooooo much easier to use fat drink straws (think McDonald's). You find the highest spot on your cake (really there should not be a 'highest' spot if you used a cake leveler on each layer), stick one straw *straight* into the cake and mark where it meets the icing. Remove and cut *ALL* straws *for that tier* the same exact size. Do not cut all straws used for all the tiersto the same height- just the ones that go into that tier - as each tier can be slightly different - Make sure when inserting them into the cake that they go in straight. Push it in a bit that is stands alone and turn the cake around observing if it is straight, then push in about 1/2 way more & repeat observation; continue like that until all straws are in straight.